The present invention relates to friction feed mechanisms for continuous and cut form paper. In particular, the invention relates to improved means for feeding cut forms to and from the information recording or reproducing region of an information handling device.
In an impact printing machine there is generally provided a cylindrical platen around which the paper is fed, a printing mechanism disposed in a printing region adjacent to the platen and an inked ribbon disposed between the printing mechanism and the platen. In operation, the printing mechanism impacts the inked ribbon and drives it against the paper on the platen to perform the printing operation. It is essential that the paper be held against the platen in the printing region so that the paper will have a firm base therebeneath, against which the printing elements can be struck. It is also important that no bulges or slack regions be formed in the paper to insure that as the paper is advanced by the feed mechanism, the portion of the paper in the printing region will move the same distance as the portion in the feed mechanism to insure accurate spacing between lines of print.
In standard typewriters these requirements are met by providing guide means which positively guide the paper along substantially its entire path around the platen and through the printing region. But in line printers of the continuous belt type, such paper guides cannot be used because in the printing region an opening or window must be provided along the entire length of the platen, since plural points anywhere along the platen may be imprinted simultaneously.
Typically, line printers are designed for use with continuous form paper. In such machines the leading edge of the continuous form is hand-fed around the platen and through the printing region and engaged with a drive mechanism downstream from the printing region, which drive mechanism serves to pull the paper through the printing region, this pulling action serving to hold the paper against the platen. The drive mechanism may be in the form of pinwheels, pressure rollers and other tractor devices which engage apertures in the edges of the paper form.
While the foregoing arrangement works fine for continuous forms, it cannot be used with cut forms in discrete sheets, since there is no means for automatically feeding such sheets through the machine. More specifically, there is no mechanism for effectively driving the sheet through the printing region and to the point at which the leading edge engages the tractor mechanism. In a conventional typewriter, this feeding is effected through a friction feed mechanism comprising friction rollers cooperating with the driven platen frictionally to drive the paper therebetween. Such friction feed mechanism is typically below the platen and serves to push the paper upwardly around the platen and to the printing region. Additional pinch rollers may then be used above the printing region to assist in guiding the paper and holding it against the platen.
Attempts to use this standard friction drive mechanism with belt-type line printers such as chains or bands for permitting the automatic feeding of discrete sheets therethrough have not been successful for several reasons. First of all, the use of a friction feed which pushes the paper through the printing region will not suffice, in and of itself, to permit automatic feeding of discrete sheets. This is because once the trailing edge of the sheet passes the friction feed mechanism, the sheet will no longer be driven. Thus, the last couple of inches of the sheet cannot be moved through the printing region. Therefore, it is necessary additionally to use some sort of auxiliary feed mechanism which engages the leading edge of a sheet downstream of the printing region for pulling the tail end of the form through the printing region. In standard typewriters this is achieved by the use of an additional set of friction rolers directly on the driven platen downstream from the printing region. But, as will be explained below, such an arrangement cannot be used in the belt-type line printer.
Secondly, the discrete sheet forms cannot be positively guided all the way through the printing region for the reasons set forth above. This means that it will be necessary that the sheet traverse an unguided or free path portion through the printing region. Where the positive guiding ceases, the leading edge of the paper will tend to diverge from the platen generally tangent thereto. This free path portion is arranged so that the sheet does not contact the print ribbon, otherwise it will foul the ribbon and cause jamming thereof, and/or create a paper jam and smudges on the paper. Since the paper sheet leaves the platen in the printing region, it must be picked up after it clears the ribbon and be guided back to the platen.
It has been found that if upper pinch rollers directly on the platen are used for this purpose and to provide the exit drive for the sheet, the leading edge of the paper must be rapidly deflected back to the platen surface to engage the pinch roller, thereby creating a bulge or hump in the paper path between the printing region and the upper pinch rollers. Such a bulge is unacceptable because once the trailing end of a sheet passes the entry friction feed so that it is no longer pushed, the pulling force exerted by the exit friction drive would first take up the slack in the paper hump or bulge before continuing to move the paper through the printing region. During this slack take-up period, therefore, line spacing in the printing region would be nonexistent or at best very uneven.